In spray paint operations, a paint fluid or resin, commonly in the form of a liquid, is mixed with one or more constituents, such as hardeners and/or liquid or solid color additives, prior to application of the mixed material to a work surface. Commonly, the user must either manually mix the constituents prior to application of the final mixture and/or provide a metered introduction of the constituents into a fluid flow to attain a desired mixture. The repeatability of generating a given fluid mixture is substantially limited by the ability of a technician to repeatedly measure and combine the constituent fluids and additives in an accurate manner to produce the desired mixture. Additionally, the consistent attention to the operation of the discrete systems of the mixed fluid delivery system requires a highly skilled or trained operator to ensure repeatable desired results during each material application cycle.
Automatic mixing devices overcome some of the shortcomings associated with manual mixing requirements but present their own drawbacks. FIGS. 3-5 show an exemplary prior art two-part fluid delivery system or fluid mixing machine that adds a catalyst or a hardener to a fluid paint stream. Such mixing machines are widely used during the coating or painting of various metal, carbon or fiber, or plastic based material parts commonly configured as automotive or vehicle body panels and the like.
In the automotive environment, such parts are most often finished with what is commonly understood as low bake temperature coatings. Prior to the advent of automatic mixing machines, a finisher or paint applicator personnel would manually add hardener to the resin or paint in a batch form and attempt to utilize the batch before expiration of the usable or pot-life of the mixture. Such pre-application preparation of the mixture requires an estimation of the total material needed to treat or coat all of the desired parts. Such activity commonly requires the personnel to estimate both fluid material consumption as well as the amount of material that the given operator can consume within the duration or pot life of the particular material mixture.
Depending on a number of commonly understood parameters including ambient temperature and humidity, constituent composition and ratios, desired product characteristics, substrate conditions, etc., the ratio of hardener to color fluid, resin or paint can commonly vary from ratios of 1:1 to less than 100:1. Such bulk batching commonly results in substantial waste with operators mixing more than adequate amounts of material to avoid “running short” or consuming all of the pre-application mixed material before all of the desired parts have been treated.
With the variable desired ratio ranges, ratio repeatability is typically only about 5% and incorrect ratios can result in complications and/or inoperability of the paint system during application of the color mixture or a less than desired and/or acceptable finished or cured paint layer. If insufficient hardener or catalyst is added to the fluid paint, the paint mixture will normally not dry or cure as desired. Excessive hardener or catalyst detrimentally impacts pot-life and can also yield undesirable or unacceptable finish part quality. Such complications commonly result in requiring that the affected parts be cleaned and retreated or repainted and/or discarded altogether. Unexpected pot-life limits can also detrimentally affect and/or damage the operability of the material applicator devices.
Many automatic mixing devices commonly use multiple electro-mechanical flow meters that monitor the individual volumes of paint or resin and hardener for ratio assurance. Such flow meters are commonly provided as two meshed gears that turn freely in the respective fluid flow. A gear tooth sensor monitors movement of the teeth of a respective gear to assess the fluid flow. Each tooth represents a specific volume. An exemplary standard volume per gear tooth is 0.12 cc/gear tooth. Understandably, other volume flow meters are available for other applications.
Many paints or resins and hardeners are relatively thin or have low fluid viscosities such that, even with the relatively close mechanical association of the gears and the corresponding housing of such flow meters, some of the fluid material can pass around and/or through the gears in a manner that detracts from the accuracy of the respective fluid measurement. Low relative fluid flow rates can also exacerbate the ability to accurately assess the respective fluid flow. Accordingly, such fluid delivery systems must be diligently monitored and/or frequently calibrated to ensure accurate assessment and monitoring of the respective constituent fluid material flows. Although frequent system calibration reduces the potential for inaccurate operation of the respective flow meters, repeated calibration of the flow sensor detracts from the “automatic” nature of such fluid delivery systems and wastes both operating time and materials.
Calibration of such automatic fluid delivery systems commonly requires a multiple step verification process. FIGS. 3-5 show an exemplary prior art automatic paint application system. During a combined fluid flow verification process, the operator must verify the volume of the paint, resin flow, and combined volume to assess the operability of the system. As shown in FIG. 3, in first step of assessing operation of the system the operator draws a sample from a designated port 20 into a graduated cylinder or beaker 22. The value of the measured volume is entered into a controller 24.
Referring to FIG. 4, this fluid measuring process is then repeated for the additive or hardener fluid path of the fluid mixing system. As shown in FIG. 4, the delivery system includes a second designated port 30 that is in fluid communication with a hardener fluid flow path. A hardener sample is acquired with another graduated cylinder 32 such that the volume of hardener delivered can also be determined or assessed. Controller 24 is in communication with a pair of toothed gear flow meters 38, 40 that electro-mechanically assess the flow of the restrictive additive and resin flows in the manner described above. These values are communicated to controller 24 as the detected flow values. The value of the acquired volumes of hardener and resin are entered into controller 24 which thereby compares the discrete measured volumes with the discrete detected flow values to calibrate the respective flow meter 38, 40 associated with delivery of the respective hardener and resin materials.
After the individual flow meters 38, 40 have been calibrated, the fluid material delivery ratio can be assessed. Referring to FIG. 5, to verify the delivery ratio between the paint material and/or resin and the hardener, the user uses two beakers 34, 36 during concurrent delivery of both the paint and/or resin fluid and the liquid hardener during operation of the delivery system. The two constituents or fluid components flow concurrently into separate beakers 34, 36. Visual inspection of beakers 34, 36 allows the user to visually and then mathematically verify the ratio between the delivery of the paint and/or resin and the hardener. After each calibration process, the user must clear or clean the dedicated sample ports 20, 30 as well as the various cylinders 22, 32, 34, 36 associated with the acquisition of the various samples.
The calibration and delivery ratio verification process is cumbersome and time consuming and includes such drawbacks that many users neglect to perform the operational verification processes. As alluded to above, neglecting confirmation of the operational integrity of the paint delivery system can result in less than desired, unexpected, and/or unacceptable constituent fluid deliver performance and yield potentially unacceptable part or application quality as well as possible damage to the underlying paint application system. Although hindering operation of the application system until completion of an operational verification process would result in more timely completion of the verification calibration (if not bypassed), mandating such verification does not resolve the inefficiencies associated with the manual verification and calibration of the various sensors and volume assessments.
Therefore, there is a need for a mixed fluid delivery system that both accurately delivers desired amounts of constituent fluids and can be quickly and conveniently assessed to verify the operational integrity of the fluid delivery system with respect to preset operating conditions.